Casings For Implantable Stimulators And Methods Of Making The Same

ABSTRACT

An implantable stimulator includes a device for delivering a stimulus and a casing having a first, metal portion and a second, portion which is formed from a plastic or polymer. A method of forming an implantable stimulator includes preparing a coil on a ferrite tube and molding a casing body on the coil, such that the coil is embedded in a wall of the casing which is formed of a plastic or polymer. Another method of forming an implantable stimulator includes forming an annular metal connector and molding a plastic or polymer casing body on the metal connector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority toU.S. application Ser. No. 11/043,399, filed on Jan. 26, 2005, publishedas U.S. Patent Publication No. 2006/0167521, now U.S. Pat. No. ______,the contents of which are incorporated herein by reference.

BACKGROUND

Implantable stimulators and microstimulators, also known as BION®devices (where BION® is a registered trademark of Advanced BionicsCorporation, of Valencia, Calif.), are typically characterized by asmall, cylindrical housing which contains electronic circuitry thatproduces electric currents between spaced electrodes. Thesemicrostimulators are implanted proximate to target tissue, and thecurrents produced by the electrodes stimulate the tissue to reducesymptoms or otherwise provide therapy for various disorders. Animplantable, battery-powered medical device may be used to providetherapy for various purposes including nerve or muscle stimulation. Forexample, urinary urge incontinence may be treated by stimulating thenerve fibers proximal to the pudendal nerves of the pelvic floor;erectile or other sexual dysfunctions may be treated by providingstimulation of the cavernous nerve(s); and other disorders, e.g.,neurological disorders caused by injury or stroke, may be treated byproviding stimulation of other appropriate nerve(s).

By way of example, a microstimulator known in the art is described inU.S. Pat. No. 5,193,539, “Implantable Microstimulator,” which patent isincorporated herein by reference in its entirety. The '539 patentdescribes a microstimulator in which power and information for operatingthe microstimulator are received through a modulated, alternatingmagnetic field in which a coil is adapted to function as the secondarywinding of a transformer. The induction coil receives energy fromoutside the body and a capacitor is used to store electrical energywhich is released to the microstimulator's exposed electrodes under thecontrol of electronic control circuitry.

In U.S. Pat. Nos. 5,193,540 and 5,405,367, which patents areincorporated herein by reference in their respective entireties, astructure and method of manufacture of an implantable microstimulator isdisclosed. The microstimulator has a structure which is manufactured tobe substantially encapsulated within a hermetically-sealed housing inertto body fluids, and of a size and shape capable of implantation in aliving body, with appropriate surgical tools. Within themicrostimulator, an induction coil receives energy from outside the bodyrequiring an external power supply.

In yet another example, U.S. Pat. No. 6,185,452, which patent islikewise incorporated herein by reference in its entirety, there isdisclosed a device configured for implantation beneath a patient's skinfor the purpose of nerve or muscle stimulation and/or parametermonitoring and/or data communication. Such a device contains a powersource for powering the internal electronic circuitry. Such power supplyis a battery that may be externally charged each day. Similar batteryspecifications are found in U.S. Pat. No. 6,315,721, which patent isadditionally incorporated herein by reference in its entirety.

Other microstimulator systems prevent and/or treat various disordersassociated with prolonged inactivity, confinement or immobilization ofone or more muscles. Such microstimulators are taught, e.g., in U.S.Pat. Nos. 6,061,596 (Method for Conditioning Pelvis Musculature Using anImplanted Microstimulator); 6,051,017 (Implantable Microstimulator andSystems Employing the Same); 6,175,764 (Implantable MicrostimulatorSystem for Producing Repeatable Patterns of Electrical Stimulation;6,181,965 (Implantable Microstimulator System for Prevention ofDisorders); 6,185,455 (Methods of Reducing the Incidence of MedicalComplications Using Implantable Microstimulators); and 6,214,032 (Systemfor Implanting a Microstimulator). The applications described in theseadditional patents, including the power charging techniques, may also beused with the present invention. The '596, '017, '764, '965, '455, and'032 patents are incorporated herein by reference in their respectiveentireties.

SUMMARY

Implantable stimulators described herein include a device for deliveringa stimulus and a casing having a first, metal portion and a second,portion which is formed from a plastic or polymer. Methods of forming animplantable stimulator described herein include preparing a coil on aferrite tube and molding a casing body on the coil, such that the coilis embedded in a wall of the casing which is formed of a plastic orpolymer. Other methods of forming an implantable stimulator describedherein include forming an annular metal connector and molding a plasticor polymer casing body on the metal connector.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of the presentinvention and are a part of the specification. The illustratedembodiments are merely examples of the present invention and do notlimit the scope of the invention.

FIG. 1 is a diagram of a stimulator and external controlling deviceaccording to principles described herein.

FIG. 2 illustrates a coil and ferrite tube for an implantable stimulatoraccording to principles described herein.

FIG. 3 illustrates a stimulation capacitor for an implantable stimulatoraccording to principles described herein.

FIG. 4 illustrates a casing for an implantable stimulator incorporatingthe coil and ferrite tube of FIG. 2 and the capacitor of FIG. 3according to principles described herein.

FIG. 5 illustrates a connector for another implantable stimulator casingaccording to principles described herein.

FIG. 6 illustrates another implantable stimulator casing according toprinciples described herein and including the connector of FIG. 5.

FIG. 7 illustrates another alternative implantable stimulator casingaccording to principles described herein and including the connector ofFIG. 5.

FIG. 8 is an alternative view of the stimulator casing of FIG. 7according to principles described herein.

FIG. 9 is a flowchart illustrating one method of forming a stimulatorcasing according to principles described herein.

FIG. 10 is a flowchart illustrating another method of forming astimulator casing according to principles described herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

The present specification describes, among other things, a polymer orplastic casing for an implantable stimulator. With a plastic casing, itbecomes possible to injection mold the casing in a wide variety ofdesired configurations at minimal cost. Additionally, forming the casingof plastic avoids the need for laser welding and brazing processes whichhave, in the past, been relatively expensive and difficult parts of thestimulator fabrication process. Moreover, portions of the stimulator canbe built into the plastic casing. For example, the plastic casing can bemolded over and around some components of the stimulator to realize anumber of advantages that will be described in more detail below.

An implanted stimulator may deliver an electrical current to surroundingtissue to stimulate that tissue for therapeutic purposes. Additionallyor alternatively, a stimulator may deliver a chemical or drug tostimulate target tissue for therapeutic purposes. While electricalstimulators that output a stimulating current are the most predominantform of implanted stimulators, as used herein and in the appendedclaims, the term “stimulus” or “stimulation” will be used to referbroadly to electrical, chemical, mechanical or other output of animplanted stimulator for therapeutic purposes.

When a stimulating current is used as the stimulus, the current outputby an implanted stimulator is not constant, but is delivered in aregular cycle. Consequently, there are a number of parameters thatcharacterize the current that is output by the implanted stimulator. Forexample, the stimulating current will have a frequency, amplitude andpulse width. These parameters can be adjusted to tailor the stimulationto the needs of a particular recipient patient. The stimulating currentmay also be delivered in bursts and have a duty cycle that describes thelength and frequency of the current bursts.

Some patients receive a stimulator to control or mask chronic pain. Insuch patients, the stimulator may create a tingling sensation throughouta particular painful region of the body known as paresthesia. The size,intensity and character of the paresthesia may be controlled byadjusting the parameters of the stimulating current.

In addition to tailoring the stimulation parameters, the size andplacement of a stimulator are also important to the effective treatmentof a patient. Microstimulators are smaller than conventionally sizedstimulators and are more easily implanted in a patient. Microstimulatorsmay be injected through a large bore needle or cannula, or placed via asmall incision in the skin. As used herein and in the appended claims,unless otherwise specifically denoted, the terms “stimulator” and“microstimulator” will be used interchangeably to refer to anyimplantable medical device that may be implanted within a patient toprovide a stimulus.

FIG. 1 shows an exemplary implantable stimulator (10) and an exemplaryexternal device (20) that is used, for example, to provide power to, andcommunicate with, the stimulator (10) after the stimulator is implantedin a patient. As will be described in more detail below, the externaldevice (20) may take any of several forms, including, but not limitedto, a base station and chair pad or a remote control unit.

The implantable stimulator (10) may be any type of implantable medicaldevice. For example, the implantable stimulator (10) may be animplantable microstimulator. An exemplary, but not exclusive,implantable microstimulator is the BION® microstimulator (AdvancedBionics® Corporation, Valencia, Calif.) which may be configured tostimulate tissue to alleviate urinary incontinence, reduce pain, orotherwise provide therapy for various disorders. Other examples ofimplantable stimulators include, but are not limited to, spinal cordstimulators (SCS), cochlear implants, and deep brain stimulators.

The implantable stimulator (10) is implanted in the target tissue areaof a patient. The external device (20) is then used to communicate with,and provide power to, the implanted stimulator (10). Such communicationmay include, but is not limited to, transcutaneously transmitting datato the stimulator (10), receiving data from the stimulator (10),providing power for the stimulator (10), transferring power to arechargeable battery (16) in the stimulator (10), and/or providingrecovery power to the rechargeable battery (16) when the battery hasbeen depleted to zero volts.

As illustrated in FIG. 1, the stimulator (10) may include a number ofcomponents as best suits a particular application. In general, thestimulator (10) includes a stimulating capacitor (15) and two or moreelectrodes (22, 24) configured to stimulate target tissue with astimulation current, as mentioned above. The stimulator (10) may alsoinclude additional and/or different electronic components (14)configured to perform a variety of functions as best serves a particularapplication.

A battery (16) may be included and configured to supply the stimulator(10) with power. The battery (16) may be a primary battery, arechargeable battery, a capacitor, or any other suitable power source.In some examples, however, no battery (16) is included, with thestimulator (10). In such a case, the stimulator is powered exclusivelyby the external device (20).

The communication between the external device (20) and the implantedstimulator (10) uses a coil or inductor (18) in the stimulator (10). Acorresponding coil (34) is part of the external device (20). The coil(18) in the stimulator is configured to receive and/or emit a magneticfield that is used to communicate with, or receive power from, theexternal device (20),

The exemplary external device (20) of FIG. 1 includes control circuitry(39) and an antenna/charging coil (34) configured to emit and/or receivea magnetic field that is used to communicate with the implantablestimulator (10). In some examples, the antenna/charging coil (34) andthe stimulator's coil (18) communicate via a bidirectional telemetrylink (48). The bidirectional telemetry link (48) may be known as a RadioFrequency (RF) telemetry link. The data transmitted over the telemetrylink (48) may include configuration bits, programming bits, calibrationbits, and/or other types of data. The signals that are sent between theexternal device (20) and the stimulator (10) may be modulated usingfrequency shift keying (FSK), on-off keying (OOK), or any other type ofmodulation scheme.

And, as mentioned, the coils (18, 34) may also be used to transfer powerto the implanted stimulator (10). For example, the external device (20)may be a chair cushion on which a patient sits, or a box on a belt wornby a patient, to bring the external device (20) into proximity with thestimulator implanted in the patient. Power is then transcutaneouslytransferred from the external device (20) to the implanted stimulator(10) using the coils (18, 34) as a transformer.

Consequently, the coil (18) is clearly a very significant component ofthe stimulator (10). The greater the inductance of the coil (18) thebetter able the coil (18) is to communicate with, and receive powerfrom, the external device (20). However, increasing the inductance ofthe stimulator coil (18) requires increasing the size of the coil (18).Ultimately, this may mean increasing the size of the stimulator (10) toaccommodate a larger coil (18). Unfortunately, a larger stimulator (10)is not desirable. A larger stimulator, for example, will require a moreinvasive implantation procedure and may be less comfortable to thepatient.

However, according to principles described herein, the size of the coil(18) can be increased without increasing the size of the stimulator(10). As will be described in more detail below, the coil (18) is formedwith an outer diameter that is just a little smaller than the outerdiameter of the stimulator casing. The casing is then molded of plasticor polymer around the coil (18). The coil (18) is thus embedded insidethe wall of the casing for the stimulator and is consequently largerthan would be possible if the coil (18) had to fit inside the interiorof the casing.

As shown in FIG. 2, the coil (18) is wound around a ferrite tube (50).In some examples, the tube (50) is machined with a groove along itcentral length and being wider at the ends (51). This may be referred toas a dumbbell-shape and facilitates the winding and positioning of thecoil (18) at the center of the ferrite tube (50). In some examples, thetube (50) may not be ferrite, but made from some other material such asplastic. A ferrite tube will increase the coil inductance, but will alsomake the device incompatible with Magnetic Resonance Imaging (MRI). Ifthe device is implanted at a location that is shallow or easy to access,using a material other than ferrite as the tube (50) may be helpful bymaking the device compatible with a MRI.

Two leads (52) that connect to the coil (18) will be left extending fromthe coil/tube assembly (18,50). These leads (52) will also extendthrough the plastic of the stimulator casing when the casing is formedover the coil (18) and ferrite tube (50). Consequently, even thought thecoil (18) will be embedded in the casing of the stimulator, the coil(18) can still be driven or a signal received from the coil via theleads (52).

Another component of the stimulator that may be formed and then embeddedin the plastic casing, according to principles described herein, is thestimulation capacitor (15). As shown in FIG. 3, the capacitor (15) isformed in a cup or enclosure around which an end of the stimulatorcasing will eventually be molded.

The capacitor (15) is formed, for example, on a metal base (60). Themetal base (60) may be, for example, titanium. The capacitor (15) may beformed, for example, of tantalum.

A wire or lead (61) is connected to the capacitor (15) so that thecapacitor (15) can eventually be connected to the electronics of thestimulator. The lead (61) may be welded, for example, to the capacitor(15). A capacitor typically has two terminations. In the present case,one termination is the wire or a lead (61) for connection to theelectronics of the stimulator. The other termination can be thecapacitor body surface or base (60), which can also be used as astimulating electrode.

The capacitor base (60) may be in a cup shape as shown in FIG. 3.Alternatively, a wall (62) may be formed around the capacitor base (60)and the capacitor to form the cup shape shown in FIG. 3.

In either case, the cup wall (62) may include, for example, a groove(63) around a lip of the cup. The wall (62) may also include a raisedridge (64) that runs around the upper portion of the wall (62) below oradjacent the groove (63). This groove (63) and ridge (64) will provideadditional mechanical strength when the capacitor (15) is encased in thematerial of the stimulator casing.

FIG. 4 illustrates a partially completed stimulator in which a plasticcasing (70) has been formed, e.g., molded, to encase the coil, ferritetube and capacitor described above. As shown in FIG. 4, the coil (18),wrapped on the ferrite tube (50), is aligned with the capacitor (15).The coil (18) and capacitor (15) may be aligned, for example, in a mold(not shown).

Liquid plastic or other polymer material is then injected into the mold.The plastic can be any high density, high strength, bio-compatibleplastic or polymer material. The plastic material used may be, forexample, PolyEtherEtherKetone (PEEK).

The plastic in the mold surrounds and encases the coil (18), ferritetube (50) and capacitor (15). When the plastic hardened or is cured, itforms a casing (70) for a stimulator. The casing (70) is integrated withand includes the coil (18), ferrite tube (50) and capacitor (15).

In this way, space is saved inside the casing (70) because components ofthe stimulator are now housed in the wall of the casing (70). The coil(18) is made larger without enlarging the size of the casing by beingdisposed inside the outer wall of the casing (70). The capacitor (15)can also function as one of the electrodes of the stimulator.

As shown in FIG. 4, the lead (61) for the capacitor (15) and the leads(52) for the coil (18) extend from a mouth (71) of the casing (70).These leads (61, 52) can then be connected to the electronics of thestimulator which are then placed inside the casing (70). The casing (70)is then sealed to complete the stimulator.

The mouth (71) is made of metal, for example, titanium. In the finalassembly of the stimulator, laser welding is used to seal the casing(70) and form a hermetically sealed device. For example, a metal casedbattery having a flange can be laser welded to the mouth (71) tocomplete the final hermetic seal.

FIG. 9 is a flow chart documenting this method of forming a stimulatorhousing. As shown in FIG. 9, the coil is prepared on the ferrite tube(step 90). As noted above, this may be facilitated by machining thecentral portion of the ferrite tube where the coil is disposed to have asmaller outer diameter than the ends of the tube.

Next, the capacitor is prepared (step 91). As described above, this mayinclude forming a tantalum capacitor on a metal base, such as titanium,and welding a wire or lead to the capacitor.

The body of the casing is then formed, for example, by injection moldinga plastic or polymer (step 92). The coil and ferrite tube, and thecapacitor, are placed in the injection mold so as to become embedded inthe completed body of the stimulator casing.

Lastly, the coil and capacitor are connected to the electronics of thestimulator (step 93). The casing can then be sealed to complete thestimulator.

As noted above, one of the advantages of using plastic or polymermaterial and injection molding a stimulator casing is the ability toeasily provide a wide variety of casing shapes and configurations. Aswill be described next, metal and plastic components can be combined toadvantageously form a stimulator casing.

FIG. 5 illustrates a connector for another implantable stimulator casingaccording to principles described herein. As shown in FIG. 5, a metalconnector (80) can be used in conjunction with injection molding of apolymer or plastic material to form a casing for an implantablestimulator.

The metal connector (80) may be made, for example, from titanium. In theexample of FIG. 5, the shape of the connector (80) is that of agenerally-rectangular annulus. A leaf or ridge (81) extends from oneside of the connector (80) and runs around the perimeter of theconnector (80). One or more grooves, ribs or edges (82) may be formed onthe leaf (81).

The rest of the casing will be injection molded onto the connector (80)and will be made of a plastic or polymer material such as that describedabove. The leaf (81) with the groves (82) will provide additionalsurface area of contact between the metal connector (80) and the plasticportion of the casing. This will provide the interface between the twocomponents with greater mechanical strength. A completed casing usingthe connector (80) is illustrated in FIG. 6.

FIG. 6 illustrates another implantable stimulator casing according toprinciples described herein and including the connector of FIG. 5. Asshown in FIG. 6, a casing body (86) has been formed on the connector(80). As described above, the casing body (86) can be injection moldedor otherwise formed on the connector (80) from a plastic or polymermaterial. Since injection molding is performed at very high temperaturesand under high pressure, the interface (87) between the metal connector(80) and the plastic body (86) can be very tight, even hermetic.

To complete the stimulator, the necessary electronics and othercomponents are loaded into the casing (86). A feed-through head (83) canthen be laser welded to the connector (80) to seal the casing andcomplete the stimulator.

FIG. 7 illustrates another alternative implantable stimulator casingaccording to principles described herein and including the connector ofFIG. 5. As shown in FIG. 7, a connector (80), like that illustrated inFIG. 5, can be used at both ends of a molded, plastic or polymer casingbody (85). As before, the leaves (81) of the connectors (80) are used tosupport and create a hermetic interface with the molded casing body(85).

The metal connectors (80) can be sealed by laser welding, as describedabove, to seal the stimulator. The metal connectors (80) may alsofunction as electrodes for the completed stimulator.

FIG. 8 is an alternative view of the stimulator casing of FIG. 7according to principles described herein. As shown in FIG. 8, a plasticor polymer casing body (85) is formed between two metal connectors (80)at either end of the stimulator. The plastic or polymer casing (85) mayalso cover the sides of the connectors (80) to increase the overallmechanical strength of the casing.

FIG. 10 is a flow chart documenting this alternative method of forming astimulator casing. As shown in FIG. 10, the metal connector is firstprepared (step 95). The metal connector can be considered the foundationof the stimulator casing.

As described above, a leaf with grooves is formed on the metal connector(step 96). This increases the surface area between the metal connectorand the plastic or polymer portion of the casing to improve themechanical strength of the whole. In some examples, only a single metalconnector is prepared. In other examples, two metal connectors areprepared, one for each end of the stimulator casing.

The connector(s) are then, for example, placed in a mold and theremainder of the casing body is formed on the connector(s) from aplastic or polymer material (step 97). This is done, for example, byinjection molding.

The remaining components of the stimulator can then be installed in thecasing. When internal construction of the stimulator is completed, thecasing can then be sealed (step 98) by, for example, laser welding afeed-through head to the open end of the connector(s).

The preceding description has been presented only to illustrate anddescribe embodiments of the invention. It is not intended to beexhaustive or to limit the invention to any precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching.

1. A device comprising: nerve stimulator circuitry configured to output electric currents suitable for stimulating a nerve; and an implantable casing comprising a first portion having a first plastic or polymeric wall that defines a first cross section, and a second portion having a second metallic wall that defines a second cross section, wherein the first wall is hermetically-sealed to the second wall to dispose the first portion adjacent to the second portion.
 2. The device of claim 1, wherein: the first wall defines a first interior cavity; the second wall defines a second interior cavity; and the first interior cavity and the second interior cavity communicate to define a receptacle dimensioned to encase the nerve stimulator circuitry.
 3. The device of claim 1, wherein: the first portion comprises a first collection of plastic or polymeric walls that are joined together to define a first rounded rectangular cross section; and the second portion comprises a second collection of metallic walls that are joined together to define a second rounded rectangular cross section.
 4. The device of claim 3, wherein the first rounded rectangular cross section is disposed adjacent to the second rounded rectangular cross section to define an elongate casing having a generally uniform rounded rectangular cross section.
 5. The device of claim 1, wherein the second portion further comprises a second plastic or polymeric wall that encases the second metallic wall.
 6. The device of claim 1, further comprising a interface between the first wall and the second wall, wherein the first wall and the second wall overlap at the interface.
 7. The device of claim 4, wherein the interface between the first wall and the second wall includes a surface of a groove or a rib, wherein the surface is generally perpendicular to the overlap of the first wall and the second wall.
 8. The device of claim 4, wherein: the first portion comprises a first generally tubular portion; the second portion comprises a second generally tubular portion; and the interface comprises an annular interface joining open ends of the first generally tubular portion and the second generally tubular portion.
 9. The device of claim 1, wherein the first portion comprises a coil embedded within the first plastic or polymeric wall.
 10. The device of claim 1, wherein the first portion further comprises an elongate ferrite core disposed within the embedded coil.
 11. The device of claim 1, further comprising a capacitor electrically connected to the nerve stimulator circuitry, wherein at least a portion the capacitor is embedded within the first plastic or polymeric wall.
 12. The device of claim 11, wherein the capacitor comprises a cup-shaped member that is dimensioned to cap the first cross section of the first portion.
 13. A method of forming an implantable nerve stimulator comprising: forming an implantable casing for the implantable nerve stimulator, comprising molding a plastic or polymer to form a first plastic or polymeric wall that defines a first cross section and to form an interface between the first wall and a second metallic wall that defines a second cross section, wherein the first wall is hermetically-sealed to the second wall via the interface.
 14. The method of claim 13, wherein: the first plastic or polymeric wall defines a first interior cavity; the second metallic wall defines a second interior cavity; and the first interior cavity communicates with the second interior cavity.
 15. The method of claim 14, wherein the method further comprises inserting nerve stimulator circuitry configured to output electric currents suitable for stimulating a nerve into one or both of the first interior cavity and the second interior cavity.
 16. The method of claim 13, wherein: the first wall defines a first generally rounded rectangular cross section; the second wall defines a second generally rounded rectangular cross section; and the first rounded rectangular cross section is aligned with the second rounded rectangular cross section to define an elongate casing having a generally uniform rounded rectangular cross section.
 17. The method of claim 13, wherein molding comprises injection molding the first wall.
 18. The method of claim 13, wherein molding the plastic or polymer comprises embedding a coil within the first plastic or polymeric wall.
 19. The method of claim 13, wherein molding the plastic or polymer comprises embedding a capacitor within the first plastic or polymeric wall.
 20. The method of claim 13, wherein molding the plastic or polymer comprises molding the plastic or polymer around a ferrite core.
 21. The method of claim 13, wherein molding the plastic or polymer comprises molding the plastic or polymer to be in contact with a surface of a groove or a rib on the second metallic wall. 